The capture, recognition, detection, identification or quantitation of one or more chemical or biological entities is useful in the fields of recombinant DNA, human and veterinary medicine, agriculture and food science, among others. In particular, these techniques can be used to detect and identify etiological agents such as bacteria and vira, to screen bacteria for antibiotic resistance, to aid in the diagnosis of genetic disorders and to detect cancerous cells.
The state-of-the-art nucleic acid hybridization assay techniques generally involve hybridization with a labelled form of a complementary polynucleotide probe. Hybridization between particular base sequences or genes of interest in the sample nucleic acid and labelled probe is determined by detection of the labelled hybrids. The preparation of labelled probe generally involves the enzymatic incorporation of radiolabelled or modified nucleotides or chemical Preparation of labelled probes is often time consuming and expensive and has to be carried out without destroying the ability of the probe to detectably hybridize with its complementary Sequence.
Reagents for directly detecting the polynucleotide duplex formed as a result of hybridization between the sample and probe and thereby avoid the chemical labelling of the probes, would overcome this problem.
The generation of specific polyclonal antibodies that will bind double-stranded nucleic acid but not single-stranded nucleic acid is complicated by the fact that polyclonal antisera may contain antibodies that will cross-react with single-stranded nucleic acid. Polyclonal antisera may also contain naturally occuring antibodies to single-stranded nucleic acid or antibodies to single-stranded nucleic acid arising as a result of the immunization.
Monoclonal antibody technology can provide a means to select an antibody with desired affinity and specificity which will overcome the problems discussed above. Such monoclonal antibodies which will selectively bind double-stranded DNA (U.S. Pat. No. 4,623,627) or DNA-RNA hybrids (U.S. Pat. No. 4,833,084) have been prepared and used in the detection of duplexes formed between particular base sequences of interest in the sample nucleic acid and a probe with a known complementary sequence.
A new alternative arising from the construction of the nucleic acid analoque PNA (Peptide Nucleic Acid), is to use a PNA oligomer as a detection probe and generate antibodies that bind to PNA-nucleic acid complexes.
Peptide Nucleic Acids (PNAs) are described in WO 92/20702 as compounds comprising a polyamide backbone bearing a plurality of ligands such as naturally occuring nucleobases attached to a polyamide backbone through a suitable linker. It has recently been shown that PNA in which the backbone is structurally homomorphous with the deoxyribose backbone and consists of N-(2-aminoethyl)glycin units to which the nucleobases are attached can hybridize to complementary oligonucleotides to form PNA-nucleic acid complexes (Egholm et al., Nature, vol 365, 566-568 (1993)).